Methods of bonding polyethylene



14, 1961 T. c. MORRIS ET AL 3,008,863

METHODS OF BONDING POLYETHYLENE Original Filed June 24, 1954 Inventors Th omas G. M0 rPZ'S DQCQ Edith J.Morrz'5,fidmx.

Eric G. Johnson By #2926" Ait orney United rates Patent F 3,008,863 METHODS OF BONDING POLYETHYLENE Thomas C. Morris, deceased, late of Lexington, Mass., by Edith J. Morris, administratrix, Lexington, and Eric C. Johnson, Somerville, Mass, assignors to 13.13. Chemical Co., Boston, Mass, a corporation of Massachusetts Original application June 24, 1954, Ser. No. 439,122, new Patent No. 2,894,925, dated July 14, 1959. Divided and this application Jan. 29, 1959, Ser. No. 789,845

5 Claims. (Cl. 156339) This invention relates to a method of forming joints between polyethylene or polyethylene coated sheet materials.

This application is a division of our copend-ing application Serial No. 439,122, filed June 24, 1954, now United States Letters Patent No. 2,894,925, which is a continuationin-part of our copending application Serial No. 377,- 162, filed August 28, 1953.

Polyethylene plastic material possesses many desirable characteristics including inertness to most chemicals and solvents at ordinary temperatures, toughness and flexibility. Particularly in the form of relatively thin sheets polyethylene has found extensive use for containers or liners of containers, in coverings and in other allied uses.

Many of these uses require that a seam be formed between two polyethylene surfaces or between a polyethylene surface and another surface. The waxy paraifinlike character of polyethylene surfaces interferes with adhesion by most of the commonly employed adhesive or coating agents. It has been observed also that certain adhesives may form a bond which is of acceptable strength for a short period after completion but which, within a period of at most a few days, weakens to such an extent that the bonded surfaces may fall apart. Because of this difiiculty with adhesive bonding, the formation of seams or joints between polyethylene surfaces has, in substantial measure, been performed by fusing the surfaces together under heat and pressure. Very careful control is necessary for this type of joining in order that the polyethylene may not be melted to such an extent as to squeeze out the polyethylene from between the sealing members, while at the same time adequate heat and pressure must be applied to form a continuous bond. Unlike vinyl resins, polyethylene surfaces cannot be joined electronically, that is, the dielectric characteristics of polyethylene are such that subjecting it to a high frequency electric field will not induce bonding heat internally. Because of the degree of control required, heat sealing of thin sheet polyethylene to itself or other surfaces tends to be restricted to relatively simple joining operations.

It is a feature of the present invention to provide a new method for forming a strong union between a thermoplastic composition useful as an adhesive and a polyethylene surface.

According to the present invention there is provided a method of bonding polyethylene surfaces involving use of a heat softened or molten adhesive having at elevated temperatures at least limited solvent power toward the polyethylene. The adhesive composition is applied in hot molten condition at a temperature well above the melting point of polyethylene to be bonded, and in quantity to carry suflioient heat to melt the surface portions only of the polyethylene to cause mutual solution of the adhesive and polyethylene surface portions. When the joint cools, the adhesive composition adheres firmly to polyethylene and other surfaces to form a strong, flexible joint.

The invention will be described further in connection with the accompanying drawings forming part of the disclosure, in which FIG. 1 is an angular view of an adhesive supply and 3,008,863 Patented Nov. 14, 1961 2 control rod in coil form useful for practicing the method of the present invention with a portion of the rod uncoiled and inserted into a passageway for softening and dispensing the adhesive; and

FIG. 2 is a view with parts broken away of the adhesive rod disposed as a piston in a complementary passageway showing the cooperative relation between the body of solid adhesive and the walls of the passageway for controlling flow of adhesive through the passageway to the point of application.

As shown in FIG. 1, a thermoplastic adhesive rod 10 for direct through-feed adhesive dispensing is an elongated self-supporting body of solid, thermoplastic adhesive having a substantially uniform gross cross section complementary to the cross section of the entrance to the heated softening and dispensing passageway 12. The solid self-supporting rod 10 is shown coiled in overlapping layers 13 on a spool 14 from which it is fed to the melting and dispensing passageway 12. The spool 14 comprises a relatively large diameter hub member 16 and side flanges 18 and is rotatably mounted on a supporting shaft 20 which is fitted in the slotted upper ends 22 of a bifurcated supporting bracket 24. The adhesive rod 10, after it is uncoiled from the spool, passes through a trough 26 having side walls 28 and a bottom wall 30 supported by a post 32 and into the bite of toothed or notched feed rolls 34 which firmly grip it for applying axial pressure to the rod 10. From the feed rolls 34 the rod 10 passes through a guide bushing 36 and into the entry end of the passageway 12 in the heating and applying member.

As shown in FIG. 2, the passageway 12 comprises a body portion 38 in one side of which is disposed a heating element 40 to supply heat through the body portion 38 to the passageway 12. The adhesive rod 10 effectively fills the entrance portion of the passageway 12, any slight gap between the rod 10 and the walls of the passageway 12 being sealed by softened or molten material 42. When moved forward the rod 10 bears uniformly against the full cross section of adhesive whether incompletely or wholly in fluid form in the forward portions of the passageway. The uniform bearing of the rod against the entire cross section of adhesive in the passageway insures orderly progress of adhesive through the passageway which constitutes an important advantage of direct through feed adhesive dispensing.

The effective seal between the solid rod and the walls of the passageway creates a relation between them such that the rod 10 moves into the passageway 12 at the same time that an equivalent volume of heat softened adhesive leaves the dispensing end 44 of the passageway 12 through opening 46 and is spread on a work piece 48 moving beneath it. When movement of the rod 10 is halted it aids in retaining softened adhesive within the passageway 12. Thus the rod 10 serves as a supply and/or control member in the direct through-feed adhesive dispensing system and gives particularly advantageous operational characteristics when the system is used in combination with automatic or semi-automatic machines. To function as such control it is important that the rod have an indefinite length and that the rod be capable of being uncoiled from the spool or reel '14 without cracking. It is necessary that the rod in the coil retain its cross section substantially unchanged on storage and that it not adhere to adjacent coils in order that the rod may be uncoiled from the spool in a cross sectional shape complementary to the cross sectional shape of the passageway 12.

A preferred adhesive rod or strip for practicing the method of the present invention involves combination and proportioning of polyethylene, an isobutylene polymeric material and a hydrocarbon resin having, at elevated temperatures, limited solvent action on the polyethylene. These components are combined in proportions which give to the adhesive in molten condition a viscosity enabling it to be spread and to enter into intimate engagement with surfaces to be bonded, controlled solvency towards a polyethylene resin surface to provide an integrating action between the deposited body of adhesive and the polyethylene surface to be adhered, and a consistency of the materials at a joint which aids in holding them together prior to final setting up of the cement. The combination of components also provides a flexibility of bond after cooling and setting up of the adhesive which reduces localized shearing forces at the juncture between the adhesive and polyethylene surface and within the adhesive layer itself to provide a desirably strong linking action.

A preferred hydrocarbon resin is a polyterpene resin, and specifically a B-pinene polymer such as that sold under the trademark Piccolite. This polymeric material is made in a wide range of melting points, the preferred polymers being those having a melting point of 85 to 125 C. This material exerts in molten form substantial solvent action on the polyethylene resin. Other hydrocarbon resins which possess substantial sol vent action in molten condition include resinous polymerization products obtained by catalytic polymerization of mixed unsaturated monomers derived from cracked petroleum, and the resin separated from Utah type resinbearing coal which consists essentially of carbon and hydrogen, has an average molecular weight of about 1,000, a refractive index of 1.544, a specific gravity of from 1.03 to 1.06 and a melting point of from 165 to 180 C.

The polyethylene component of the adhesive composition is a relatively high molecular weight of polyethylene, i.e., a resinous polyethylene as distinguished from a wax or grease. It is preferred to employ polyethylene materials having molecular weights in the range of from about 7,000 to about 21,000 as determined by viscometric means using a solution of the polyethylene in tetralin at 130 C. and calculating the molecular weight by the following equation:

where M equals weight average molecular weight, n equals relative viscosity, C equals base molar concentration of polymer in tetralin at temperature of determin tion equals 4.0 gms. per liter at 130 C. and K equals 4.03 l gms. per liter at 130 C. In the composition it appears that the polyethylene is fluxed and dissolved by the hydrocarbon resin and that by its presence in the hydrocarbon resin it controls the solvent power of the resin towards further dissolving ability towards polyethylene. In the solidified adhesive it appears also to serve as a reinforcing filler to reduce cold flow.

The isobutylene polymeric material may be a high molecular weight rubbery polyisobutylene, i.e. a material having a molecular weight of the order of about 100,000 or may be the material known as butyl rubber, that is, a sulphur vulcanizable rubbery copolymer of isobutylene and a diolefin, usually isoprene or butadiene, in approximately the proportions of 98 parts isobutylene to two parts of the diolefin. The isobutylene polymeric material gives a flexibility and resistance to cracking to the composition which is important to a rod adhesive of this nature for direct through-feed adhesive dispensing. In addition the isobutylene polymeric material cooperates in molten condition with the hydrocarbon resin to insure a viscosity and smoothness in the molten composition which enables a uniform deposit of adhesive on surfaces to be joined and controls the melting characteristics of the adhesive to give to the rod the property of progressive softening by heat to fluid activated condition in direct through feed adhesive dispensing. In a layer of adhesive deposited to form a joint between surfaces it provides desirable viscosity to aid in holding the surfaces together prior to final setting up of the adhesive.

To achieve the desired combination of properties in 5 the adhesive composition it has been found important to combine the foregoing materials in the proportion of from about 15% to 60% of polyethylene, preferably 40% to 55%, from to 35%, preferably 20% to 30%, of the isobutylene polymeric material and from 20% to 60% of the hydrocarbon resin possessing in molten condition solvent action toward the polyethylene. It is possible to use mixtures of more than one hydrocarbon resin possessing the desired solvent characteristics and to use more than one type of molecular weight of the isobutylene polymeric material. It is important, however, in combining these materials to select components of sufficiently high molecular weight and melting point that the adhesive composition is substantially dry, that is, substantially tack free and dimensionally stable at ordinary room temperature.

Other materials may be added including antioxidants or substances which impart special properties such as very fine mineral fillers including calcium silicate, carbon blacks, and the like. Heat advancing phenolic resins or rosin-maleic anhydride adducts may be incorporated in limited amounts, e.g. up to 25%, to give improved metal adhesion. Vulcanized oil, that is, factice, may also be incorporated in limited amounts up to 10%, to increase tack.

The hydrocarbon resin, isobutylene polymeric material, polyethylene and other components are mixed and melted together with positive agitation, for example in 2. Reed mixer. A convenient procedure involves melting the hydrocarbon resin in the mixer, adding the isobutylene polymeric material and agitating until smooth and thereafter adding the polyethylene and other materials and continuing the agitation until the composition is smooth. At this point the molten material may be extruded directly as a rod or cooled and optionally sheeted out for subsequent use as a hot melt adhesive or extrusion as a rod adhesive.

The resulting rod adhesive is dimensionally stable, possesses flexibility for coiling and uncoiling and is sufficiently firm for feeding in a direct through feed dispensing and applying system. In the heating passageway of such a system the rod is progressively softened by heat to insure orderly controlled progress of adhesive through the passageway and is brought to fluid activated condition at the rate at which adhesive is consumed in the system.

The bonding of polyethylene surfaces by the method of the present invention involves the melting of surface portions of the polyethylene by the heat carried by the adhesive composition in order that mutual solution of the adhesive and the surface portions of the polyethylene may take place. The quantity of heat carried is a function of the weight quantity of adhesive deposited on a given area and the temperature of the adhesive deposited so that heat to melt the polyethylene may be obtained by employing a large quantity of adhesive at a relatively low temperature or by depositing a small quantity of adhesive at a relatively high temperature or intermediate quantities of adhesive at intermediate temperatures. The closeness of control of both temperature and quantity of adhesive deposited in a direct through feed dispensing and applying system using the rod adhesive of the present invention enables particularly effective bonding. Through simple adjustment of quantity and temperature of adhesive in the operation of this system it has been found that the quantity of heat supplied as molten adhesive may be closely controlled to give softening of the surface portions of the polyethylene and mixing of the adhesive and polyethylene to create a strong flexible bond presenting a uniform gradation in properties from the pure polyethylene of the surface to be bonded to the pure cement of the adhesive layer.

The following examples are given to aid in understanding the invention but it is to be understood that the invention is not restricted to the specific compositions or conditions of application or specific properties of the compositions given in the examples:

Example I Parts by weight Polyethylene (DYLT), mol. wt. 18,000 50 B-pinene polymerresin-melting point 115 C. (Piccolite S-115) 30 Copolymer of about 98 parts isobutylene and 2 parts isoprene (GRI-17) Antioxidant 2 The B-pinene polymer resin was introduced into a Reed mixer and melted by bringing its temperature to 150 C. The copolymer material was then added and mixed in and the temperature was lowered to about 125 to 130 C. When the mixture was smooth, the temperature was again raised to 150 C. and the polyethylene and antioxidant were added and mixed until the composition was smooth. The mixture was extruded as a A" rod, the extrusion temperature being maintained between 200 and 250 F.

This rod adhesive was coiled on a reel of which the core had a minimum diameter of only 2" and was readily uncoiled for use with the dispensing apparatus. The rod possessed a stifiness and hardness such that it could readily be pushed into the dispensing apparatus and was found to be eifective for the bonding of polyethylene sheet material or polyethylene coated sheet material, the temperature of application being approximately 325 F.

The rod was capable of storage on the reel for a period greater than 6 months without observable change in cross section. The brittle temperature was below 17 F. At a temperature of 325 F. the molten adhesive had a viscosity of approximately 250,000 centipoises as measured in a Brookfield viscosimeter.

Example 11 Parts by weight Polyethylene (DYJT), mol. wt. 10,000 5O B-pinene polymer resin-melting point 115 C. (Piccolite 8-115) Copolymer of about 98 parts isobutylene and 2 parts isoprene (GRI-17) 25 Antioxidant 2 This adhesive was mixed and extruded as a 4" rod by the procedure outlined in connection with Example I and was useful for the same purposes as the cement of Example I. This adhesive had a brittle temperature of F.

Example III Parts by weight The resin separated from Utah resin-bearing coal (RBH 510 consisting essentially of carbon and hydrogen, having an average molecular weight of 1,000, a refrac tive index of 1.544, and a melting point of 165-180 C. (described more fully in US. Patent 2,461,552 to Racli, February 15, 1949) 47.4 Piccolyte S40, a polymer of B-pinene having a 40 C.

melting point- 5.2 Hard brittle polymerized rosin having a melting point of 208217 F., flash point 424 F., acid number 150, and specific gravity 1.072 10.6 Triethylene glycol di-Z-ethyl butyrate (3GB) Copolymer of 9'8 parts of isobutylene and 2 parts of isoprene (GET-) d .5 Polyethylene (DYLT), mol. wt. 18,000 15 Antioxidant 2 The resin from Utah resin-bearing coal, the B-pinene polymer resin and the polymerized rosin were fluxed in a W.P. mixer at 250 F. The mixture was then cooled to 200 F. and the triethylene glycol di-2-ethyl butyrate was added and thoroughly mixed. Thereafter the copolymer of isobutylene and isoprene, the polyethylene and the antioxidant were added and combined as in the procedure set forth in Example I. This matenal was extruded as a A" rod at an extrusion temperature of 200 F. The rod so obtained had a brittle point of 34 F. and was useful for the same purposes as the rod adhesive of Example I but showed a much faster speed of set. The adhesive had a desirably low viscosity in molten condition which is believed to be due to the gel structurebreaking effect of the resin from Utah resin-bearing coal on the isobutylene-isoprene copolymer gel.

Antioxidant The Piccopale 100 is a resinous polymerization product obtained by catalytic polymerization of a mixture of unsaturated monomers derived from deep cracking petroleum. The monomers have a molecular weight approximating and are composed essentially of dienes and reactive olefins. The resin has a softening point (Ball and Ring) of approximately -C., a specific gravity at 25 C., of .970 to .975, a refractive index at 20 C. of 1.5116, an acid number less than one, an iodine value (Wijs) of 120, a bromine number of 7.3 and a molecular weight of approximately 1100.

The petroleum base resin and the B-pinene polymer were fluxed in a Reed mixer at a temperature of to C. The polyisobutylene was then added and the temperature of the mixer lowered to a point where the mixer pulled hard. Mixing was continued until a smooth blend was obtained. Thereafter the temperature was raised to about 140 to C. and the polyethylene and antioxidant were added and mixed until the composition was smooth. The mixture was extruded as a A rod.

The rod was found elfective in a direct through-feed dispensing and applying device for the bonding of polyethylene sheet material or polyethylene coated sheet material.

Example V Parts by weight Polyethylene (DYLT), mol. wt. 18,000 48.6 Copolymer of about 98 parts isobutylene and 2 parts isoprene (GR1-17) 19.4 Petroleum base resin (Piccopale 100) 29.1 Antioxidant 2.9

The Piccopale 100 was melted in a Reed mixer and the copolymer of butylene and isoprene was added and mixed in until the composition was smooth. Thereafter the polyethylene and the antioxidant were added and mixed in until the composition was smooth. The material was extruded as a A" fluted rod which had a brittle point of below 33 F.

This rod was fed to a direct through-feed adhesive dispensing and applying apparatus maintained at a temperature of 375 F. and was applied by the machine directly on a 2-mil polyethylene sheeting as a layer .002 thick, a second layer of the polyethylene sheeting being at once deposited on the adhesive layer and lightly rolled into engagement. The polyethylene sheeting employed had a molecular weight of about 19,000 and a melting point of about 230 F. The polyethylene was joined together by this procedure at a rate which could be as high as several hundred feet per minute. A strong bond was obtained with no distortion of the polyethylene sheets joined. In the bond between the sheets, the adjacent surface portions of the polyethylene sheets were dissolved and integrated with the cement so that the joined surfaces could not be separated without destruction of the sheeting.

In contrast to the above, it was found that employing the same polyethylene sheeting and adhesive rod but using a temperature of 300 F., the adhesive was deposited smoothly between the polyethylene sheets, but no effective bond was obtained.

Having thus described our invention, what we claim as new and desire to secure by Letters Patent of the United States is:

1. The method which comprises depositing on the polyethylene surface a quantity of molten composition comprising at least of polyethylene and possessing in molten form at least limited solvent power towards said polyethylene, said molten composition being deposited on said polyethylene surface at a temperature substantially above the melting point of the polyethylene, the temperature of the composition at the time of deposition and the quantity deposited on a given area of said surface carrying sufficient sensible heat and supplying the only 'heat to melt the surface portions only of said given area of said polyethylene surface to cause mutual solution of the composition and the polyethylene surface portions.

2. The method which comprises depositing on the surface of a polyethylene film a quantity of molten composition comprising from 15% to 60% by Weight of resinous polyethylene having a molecular weight of from about 7,000 to about 21,000, from 10% to 35% by weight of high molecular weight isobutylene polymeric material from the group consisting of sulphur vulcanizable rubbery copolymers of isobutylene and a diolefin in approximately the proportions of 98:2 and rubbery polyisobutylene having a molecular weight of the order of 100,000 and from to 60% by weight of an essentially hydrocarbon resin having a softening point of at least about 85 C. possessing in heated condition at least limited solvent power toward said polyethylene, said resin being selected from the group consisting of polyterpene resins having a softening point of 85 C. to 125 C., the resin separated from Utah resin-bearing coal and the resinous polymerization product obtained by catalytic polymerization of a mixture of unsaturated monomers derived from deep cracking petroleum and having a softening point (B.R.) of approximately 100 C., a specific gravity at C. of .970 to .975, a refractive index at 20 C. of 1.5116, an acid number less than one, an iodine value (Wijs) of 120, a bromide number of 7.3 and a molecular weight of approximately 1100, said molten composition being deposited on said polyethylene surface at a temperature substantially above the melting point of said polyethylene surface, the temperature of said composition at the time of deposition and the quantity deposited on a given area of said film carrying sufiicient sensible heat and supplying the only heat to melt the surface portion only of said given area of said polyethylene surface to cause mutual solution of the composition and said polyethylene surface portions.

3. The continuous method of bonding a polyethylene film to another surface which comprises depositing molten adhesive on the surface of said polyethylene film, said adhesive comprising at least 15% of polyethylene and possessing in molten form at least limited solvent power toward said polyethylene and being deposited on said polyethylene film at a temperature substantially above the melting point of the polyethylene, the temperature of said adhesive at the time of deposition and the quantity of said adhesive deposited on a given area of said film carrying sufficient sensible heat and supplying the only heat to melt the surface portions only of said given area of said polyethylene film to cause mutual solution of the adhesive and the surface portions of said polyethylene film, thereafter while said deposited adhesive is still in molten condition, pressing together said adhesive coated surface and said other surface and maintaining said polyethylene surface with the adhesive thereon in contact with said other surface until said adhesive solidifies.

4. The method of bonding together a first polyethylene film with a second polyethylene film which comprises depositing molten adhesive on successive portions of the surface of the first polyethylene film along a line to be bonded, said adhesive comprising at least 15% of polyethyene and possessing in molten form at least limited solvent power toward said polyethylene and being deposited on said first polyethylene surface at a temperature substantially above the melting point of the polyethylene, the temperature of said adhesive at the time of deposition and the quantity of said adhesive deposited carrying sufficient sensible heat and supplying the only heat to melt the surface portions only of areas along said line of said first polyethylene film and of surface portions of areas along the line to be bonded of said second polyethylene film, progressively bringing together successive portions of said first polyethylene film and said second polyethylene film to bring the deposited adhesive in contact with said second polyethylene surface to effect melting of the surface portions thereof and maintaining said polyethylene surfaces in this relation until said adhesive solidifies.

5. The method of bonding together a first polyethylene film with a second polyethylene film which comprises depositing molten adhesive on successive portions of the surface of the first polyethylene film along a line to be bonded, said adhesive comprising from 15 to 60% by weight of resinous polyethylene having a molecular weight of from about 7,000 to about 21,000, from 10% to 35% by weight of high molecular weight isobutylene polymeric material from the group consisting of sulphur vulcanizable rubbery copolymers of isobutylene and a diolefin in approximately the proportions of 98:2 and rubbery polyisobutylene having a molecular weight of the order of 100,000 and from 20% to 60% by weight of an essentially hydrocarbon resin having a softening point of at least about 35 C. possessing in heated condition at least limited solvent power toward said polyethylene, said resin being selected from the group consisting of polyterpene resins having a softening point of C. to 125 C., the resin separated from Utah resin-bearing coal and the resinous polymerization product obtained by catalytic polymerization of a mixture of unsaturated monomers derived from deep cracking petroleum and having a softening point (B.R.) of approximately 100 C., a specific gravity at 25 C. of .970 to .975, a refractive index at 20 C. of 1.5116, an acid number less than one, an iodine value (Wijs) of 120, a bromide number of 7.3 and a molecular weight of approximately 1100, said adhesive being deposited on said first polyethylene surface at a temperature substantially above the melting point of the polyethylene, the temperature of said adhesive at the time of deposition and the quantity of said adhesive deposited carrying sufficient sensible heat and supplying the only heat to melt the surface portions only of areas along said line of said first polyethylene film and of surface portions only of areas along the line to be bonded of said second polyethylene film, progressively bringing together successive portions of said first polyethylene film and said second polyethylene film to bring the deposited adhesive in contact with said second polyethylene film to effect melting of the surface portions thereof and maintaining said polyethylene surfaces in this relation until said adhesive solidifies.

References Cited in the file of this patent UNITED STATES PATENTS 2,220,545 Reinhardt Nov. 5, 1940 2,367,725 Lindh Jan. 23, 1945 2,462,977 Kitchin Mar. 1, 1949 2,569,540 Selby Oct. 2, 1951 2,622,053 Clowe Dec. 16, 1952 2,656,297 Davis Oct. 20, 1953 2,664,378 Heller Dec. 29, 1953 2,723,468 Marcy Nov. 15, 1955 2,894,925 Morris July 14, 1959 

1. THE METHOD WHICH COMPRISES DEPOSITING ON THE POLYETHYLENE SURFACE A QUANTITY OF MOLTEN COMPOSITION COMPRISING AT LEAST 15% OF POLYETHYLENE AND POSSESSING IN MOLTEN FORM AT LEAST LIMITED SOLVENT POWER TOWARDS SAID POLYETHYLENE, SAID MOLTEN COMPOSITION BEING DEPOSITED ON SAID POLYETHYLENE SURFACE AT A TEMPERATURE SUBSTANTIALLY ABOVE THE MELTING POINT OF THE POLYETHYLENE, THE TEMPERATURE OF THE COMPOSITION AT THE TIME OF DEPOSITION AND THE QUANTITY DEPOSITED ON A GIVEN AREA OF SAID SURFACE CARRYING SUFFICIENT SENSIBLE HEAT AND SUPPLYING THE ONLY HEAT TO MELT THE SURFACE PORTIONS ONLY OF SAID GIVEN AREA OF SAID POLYETHYLENE SURFACE TO CAUSE MUTUAL SOLUTION OF THE COMPOSITION AND THE POLYETHYLENE SURFACE PORTIONS. 